1. Field of the Invention
This invention relates to a rotary chuck constructed to reduce the effect of centrifugal force on work-gripping jaws.
2. Prior Art
Rotary chucks with radially movable jaws for gripping work located at the rotary axis of the chuck are commonly used for machining operations. In certain chuck constructions the jaws are moved through internal lever mechanisms, such as bell crank-type levers of which one arm engages the back of a movable jaw and the other cooperates with an axially movable lever actuator. Typically, the actuator is moved with a draw rod or tube connected through the back of the chuck and actuated by a hydraulic cylinder.
When a jaw chuck is rotated at relatively high speeds, centrifugal force tends to move the chuck jaws radially outward, in opposition to the work-gripping force applied through the jaw-actuating levers. At high speeds of rotation, such as 3500 revolutions per minute and above, the gripping force of the jaws of a chuck is substantially decreased to the extent that the ability to adequately hold the work during machining is lost. Rotating the work at high speeds, of course, reduces machining time and, hence, lowers the cost of production.
A number of approaches have been suggested for counteracting the centrifugal force acting on chuck jaws. For example, weighted slides have been provided within chucks movable in opposite directions to the jaws, and connected to the jaws with pivoted levers (see, for example, U.S. Pat. Nos. 2,657,068; 2,729,459 and 2,828,134). Pivoted rather than slidable jaws have been used, where an integral part of the jaw acts as a counterweight to offset the centrifugal force on a work-gripping portion and/or to supply force for gripping the workpiece (see, for example, U.S. Pat. Nos. 2,784,977 and 2,839,307). Separate counterbalances have been appended to the work-gripping jaws (U.S. Pat. NO. 2,982,558) and sliding weights have been provided to cam a collet into work-gripping contact in response to rotation (U.S. Pat. No. 2,367,863). In addition, separately attached counterweights of relatively dense material have been secured to jaw-actuating levers (U.S. Pat. No. 3,370,859).